Feedback control systems have been widely applied to date as a control method in control devices. As shown in FIG. 39, in a feedback control system control device 2, a feedback controller 201 outputs a manipulated variable u based on the difference between a controlled variable y of a plant 9, calculated by an adder 202, and a set point r of the controlled variable y (r−y). Also, a feedback controller PID (Proportional-Integral-Derivative) control is still dominant as this kind of feedback controller.
Herein, a controlled variable, which is an output of a plant (plant), is a variable that is measured by a measuring instrument such as a sensor, and controlled so as to be a set point. Also, a manipulated variable, which is an output of a controller, is a variable that is manipulated so as to cause a controlled variable for tracking to conform to a set point.
However, it may happen that control of the plant 9 by the control device 2 is affected by disturbance d, as shown in FIG. 40. Although, in a PID control system, the effect of disturbance can be reduced by tuning PID parameters such as proportional gain, integral time, and derivative time, it may happen that there is a trade-off relationship between set point response and disturbance response.
Also, a method whereby disturbance is estimated and compensated for using a disturbance observer is also known. For example, a model reference adaptive control system including a disturbance observer, a reference model, and a sliding mode controller is disclosed in PTL 1. In this system, by converging deviation between a state variable estimation value output from the disturbance observer and a reference state variable output from the reference model, and outputting a control input by the sliding mode controller so as to attenuate the disturbance, balance between set point response and disturbance response is achieved.